Transplantation has emerged as the preferred method of treatment for many forms of end-stage organ failure. While short-term results have improved, long-term outcomes remain inadequate. To maintain their allografts, patients must rigidly adhere to life-long treatment regimens using costly immunosuppressive agents that dramatically increase the risks of cardiovascular disease, infections and malignancies. The development of strategies to promote the acceptance of allogeneic tissues without the need for chromic immunosuppression could not only reduce the risk of these life-threatening complications, but also greatly expand the application of organ, tissue and cellular transplantation for diseases such as the hemoglobinopathies and genetic immunodeficiencies, Type I diabetes, and possibly other autoimmune diseases. We have developed novel non-myeloablative protocols using CD28 and CD40/CD154 T cell costimulation blockade-based therapeutics to permit the induction of high levels of hematopoietic chimerism in Rhesus macaques. However, in the setting of full MHC disparity, this chimerism was transient, did not confer immune tolerance to solid organ transplants, and resulted in significant immunodeficiency in transplant recipients. However, our preliminary data suggests that in the setting of increased MHC matching between transplant donors and recipients, costimulation blockade-based induction of durable chimerism and resultant tolerance to solid organ transplants is achievable, with preservation of protective immunity. The goal of this project is to build on our preliminary findings and develop and optimize strategies to induce stable macrochimerism and transplantation tolerance to renal allografts in non-human primates. Specifically, in this proposal we will determine 1) the effect of increasing MHC matching on chimerism durability and tolerance to solid organ transplants in the context of costimulation blockade-based immunosuppression, 2) the necessary components to our costimulation blockade based immunomodulation strategy in inducing durable chimerism and tolerance, and 3) the effect that depletion of recipient natural killer cells, or delivery of adoptive immunotherapy with either regulatory or conventional T cells will have on chimerism, survival of renal allografts, the anti-donor immune response and on post-transplant protective immunity. The unifying purpose of our proposal is to develop clinically applicable protocols for the induction of tolerance to solid organ allografts while preserving immune competence in the transplant recipient. PROJECT 1: Costimulation blockade, chimerism and tolerance across varying degrees of MHC disparity (Larsen, Christian P.) PROJECT 1 DESCRIPTION (provided by applicant): Immune tolerance, the phenomenon by which the allograft is accepted without immunosuppression while preserving the recipient's protective immunity, represents a solution to the problems of acute and chronic rejection and the resulting long-term reliance on toxic immunosuppressive therapies. The significant success of transplantation tolerance studies in rodent models has suggested that similar tolerance-induction techniques involving bone marrow transplant and hematopoietic chimerism could be achieved in preclinical and clinical situations, thus revolutionizing solid organ transplantation. Non-human primate models have a number of important attributes that allow them to serve as critical preclinical models in order to bridge the basic insights gained in mice and the application of these insights to patient care. Among the most prominent of the tolerance induction strategies are CD28/CD40 T cell costimulation blockade and mixed chimerism induction. By taking advantage of our ability to induce chimerism using mobilized peripheral blood stem cells from living Rhesus macaque donors, we propose to perform a systematic analysis of impact of a costimulation blockade and chimerism-based tolerance induction strategy in transplant pairs having varying degrees of MHC disparity. These studies also are focused on understanding the immune consequences of transplant, specifically on evaluating the anti-donor response and the preservation of protective immunity in the peritransplant period. The unifying purpose of our proposal is to develop clinically applicable protocols for the induction of tolerance to solid organ allografts while preserving immune competence in the transplant recipient. Specifically, the aims in this project will address 1) the effectiveness of a CD28/CD40 costimulation-blockade-based chimerism/tolerance induction protocol on transplants displaying varying degrees of MHC matching between the donor and recipient, 2) the necessary components of the immunomodulatory strategy for chimerism and tolerance induction, and 3) the efficacy of inhibiting Natural Killer cell-mediated alloreactivity in order to decrease the need for recipient conditioning and/or donor peripheral blood stem cells to promote tolerance across MHC barriers. We believe the ability to induce stable donor chimerism and immune tolerance in this transplant setting would have a large impact on the outcome of transplantation, and holds the promise of relieving many transplant recipients from the requirement for complicated life-long immunosuppressive regimens and their attendant toxicities.